1. Field of the Invention
The present invention relates to a polishing apparatus and method of polishing a ferrule end face for an optical connector, and more particularly to a technique for use when polishing the end face of a ferrule mounted to the joining part of a optical connectors that join together optical fibers, whereby a plurality of ferrule end faces are polished at one time with a uniform pressure, thereby eliminating a polishing process step, so as to both simplify and reduce the cost of polishing the ferrule end faces for an optical connector.
2. Description of the Background Art
In contrast to splicing, which provides a permanent connection between optical fibers, an optical connector is a connection joining member enabling a removable connection between optical fibers. In the past, a variety of practical optical connectors have been developed to enable connection and disconnection between optical fibers. For example, in a known single-fiber optical connector, in order to achieve a joint with little axial skew or tilt angle, an optical fiber is inserted into the center of a ceramic ferrule (i.e., a tubular reinforcement bar used for joining), and adhered in place, after which the optical connector ferrule (hereinafter simply referred to as ferrule) is inserted into a hollow tube having a precise inner diameter, the ends of ferrules being butted up against one another and screwed together by means of threads on the outside thereof. Because of its superior connection characteristics, the above-noted type of optical connector is widely used in many optical communication fields.
In an optical connector as described above, because the ferrules are directly butted up against one another, it is important that the ends of the ferrules be precisely polished, so as to lower the connection loss. Because optical connectors are used throughout an optical communications system, it is important to be able to lower the cost of the optical connector by enabling polishing in a short period of time. That is, there is a need for a technique that not only achieves highly precise optical connector characteristics, but also one that polishes the ferrule ends of an optical connector manufacturable with a low cost.
In a conventional polishing apparatus for achieving a convex spherical surface at a ferrule end face, a polishing plate formed in a concave spherical shape was held fixed, and the ferrule was fixed so as to be perpendicular to the concave spherical surface of the polishing plate. By imparting to the ferrule precession movement, comprising undulation and rotation about the center of the concave spherical surface, or forward and reverse rotation combined with undulation movement, the contact point is caused to move, thereby polishing the ferrule end face. Because of this process, there was the problem of breakage of the optical fiber connected at the rear of the ferrule by the action of the rotation or undulating movement of the ferrule. Additionally, a polishing apparatus performing such processing not only requires the formation of a polishing plate on a concave spherical surface, but also requires a highly precise mechanism to impart rotational or undulating movement to the ferrule, thereby making the polishing apparatus costly.
In general, when a bare optical fiber is inserted into a ferrule and then held in place with an optical adhesive, there is a swelling up of excess hardened adhesive on the end face of the ferrule. Thus, it is necessary to remove this adhesive agent before polishing the ferrule end face into a conex spherical shape.
Given the above, the inventor proposed a ferrule end face polishing apparatus wherein a polishing plate is caused to move in a path that describes the outer contour of the petals of a flower, this path synthesized by the revolution and autorotation of an external-tooth gear in a planetary gear mechanism having an internal-tooth sun gear and an external-tooth planet gear combined with an XY stage. This polishing apparatus is disclosed, for example, in the Japanese Patent Laid-open Application publication H6-15556. According to this polishing apparatus, after removing hardened adhesive agent from the ferrule end face without imparting rotation or undulation movement to the ferrule, the ferrule end face is polished with high precision to a convex spherical shape.
In the above-noted optical connector ferrule polishing apparatus, however, the following problems remained.
(1) Because there is a buildup of hardened adhesive agent on the end face of the ferrule to be polished, the overall length of each ferrule is different. Using the above-noted optical connector ferrule end face polishing apparatus, a plurality of ferrules are mounted to one ferrule holding jig, and pressed up against the polishing plate with a single pressure-applying mechanism. As a result, because a plurality of ferrules are polished under pressure applied by a single pressure-applying mechanism, because of the difference in the overall length of the ferrules, the pressures applied to individual ferrules differ, resulting invariations in the shape of the end faces of the ferrules. It is therefore not possible to achieve the optimum end face shape for all the ferrules mounted in the single ferrule holding jig.
(2) At the beginning of the processing step, polishing starts from ferrules that are longer. For this reason, some polishing time is required until the lengths of all the ferrules are made uniform, thereby resulting in a worsening of polishing efficiency.
(3) Because polishing starts from ferrules that are longer, in the case of polishing a ferrule end face for an optical connector, in which the polished surface area is small, a high pressure is applied to the longer ferrules during processing. For this reason, there is a tendency for the exposed surface of the optical fiber in the ferrule to become work distorted or damaged, resulting in a worsening of optical characteristics, and in particular of reflection attenuation.
(4) In polishing with a conventional polishing apparatus, because the four steps of adhesive agent removal, rough polishing, medium finishing, and a finished polishing were required, the work efficiency was extremely poor. That is, with four polishing process steps, it is necessary to perform polishing at each process step by setting proper conditions, such as the polishing film material, grit diameter, thickness, hardness and thickness of a resilient material placed on the top surface of the polishing plate, pressure applied to the ferrule, and the polishing speed, thereby resulting in an increase in the required time and cost. Additionally, the use of a diamond grit for polishing made the polishing cost high.
Accordingly, it is an object of the present invention to provide an apparatus and method for polishing the end faces of a plurality of ferrules of an optical connector at one time, in which independent pressure-applying mechanisms are provided corresponding to the individual ferrules to press them up against a polishing plate, a uniform pressure being applied to the plurality of ferrules, enabling the simultaneous polishing of the end face of a plurality of ferrules with a uniform pressure.
Another object of the present invention is to provide a, polishing apparatus and method in which, by selecting the material of a polishing slurry included in a polishing film used in polishing by the polishing apparatus, it is possible to simplify the polishing process, without using costly diamond grit, thereby enabling both simplification and cost reduction in the polishing process.
According to an aspect of the present invention, as shown in FIG. 1, an apparatus for polishing an optical connector ferrule end face is provided, wherein relative motion is imparted between an optical connector ferrule 10 and a polishing plate 4 so as to polish the end face of the ferrule 10 of the optical connector to a concave spherical surface, this polishing apparatus comprising a polishing plate 4, a polishing apparatus main unit 2 capable of freely moving the polishing plate 4 within an XY plane while rotating it, a cylinder block mechanism 3, and a height-adjusting mechanism 5 disposed above the polishing apparatus main unit 2 and having a plurality of independent pressure-applying mechanisms 13 provided individually so as to correspond to a plurality of ferrules 10, wherein the cylinder block mechanism 3 is caused to move in a direction perpendicular to the polishing plate 4 with the pressure-application mechanisms 13 holding the ferrules 10 at the end thereof.
The pressure-applying mechanism 13 may include a pressure-applying shaft 16 built into the pressure-applying mechanism 13 for applying a prescribed downward pressure with respect to the polishing plate 4 and a ferrule holding section 20 mounted at the end part of the pressure-applying shaft 16 and capable of holding the optical connector ferrule 10 with its end face in opposition to the polishing plate 4 fixed in the vertical direction with respect to the polishing plate 4.
The polishing apparatus main unit 2 may include a rotating mechanism of the polishing apparatus 4 and an XY stage 204 that freely moves a rotating mechanism of the polishing plate 4 and the polishing plate 4 within an XY plane.
According to the above-noted configuration, it is possible via a plurality of independent pressure-applying mechanisms disposed in a ring arrangement in the cylinder block mechanism to apply a pressure to the end faces of ferrules of an optical connector, using the top surface of a polishing filmon the polishing plate as a reference surface. In doing this, even if the lengths of each of the ferrules differ because of buildup of hardened adhesive agent on the end faces of the optical connector ferrules, when polishing is done the independent pressure-applying mechanisms act to apply a uniform pressure to the end faces of all the ferrules. As a result, because the ferrule end faces are polished to convex spherical surfaces, all of the plurality of ferrules can be polished with high precision and little variation therebetween.
The pressure-applying mechanism 13 may include an air cylinder 17 that applies pressure to the pressure-applying shaft 16 by means of the pressure of air supplied from an air supply source.
It is preferable that the pressure of the air supplied to the air cylinder 17 be in controlled within the range from 0.001 to 0.5 MPa.
According to the above-noted configuration, because the pressure-applying mechanisms of the cylinder block mechanism are implemented by air cylinders which press the pressure-applying shafts by means of the air pressure supplied by the air supply source, it is easy to control the setting of the pressure applied to the pressure-applying shafts. By doing this, it is possible to apply the proper pressure to the surface being processed, and to achieve an optimum shape at the end face of the ferrules.
By controlling the air pressure supplied to the air cylinders within the range from 0.001 to 0.5 MPa, it is possible to perform high-precision processing, without variation in the overall length of the ferrules and radius of curvature at the end faces thereof.
Another aspect of a polishing apparatus according to the present invention further comprises a position-limiting member 11 disposed at the bottom of the cylinder block mechanism 3, which stops the movement of the ferrule holding sections 20 at a prescribed position.
According to the above-noted configuration, by providing a position-limiting member at the bottom of the cylinder block mechanism, the polishing of the ferrules is stopped at the point at which the lengths of the ferrules are made uniform, thereby achieving uniform ferrule lengths, and enabling high-precision fixed-dimension processing of the ferrules without variation therebetween.
The polishing plate 4 may include a base plate, a resilient sheet 25 disposed on the base plate, and a polishing film 24 provided on the top of the resilient sheet 25.
The above-noted resilient film 25 can be made of rubber of a uniform thickness.
The polishing film 24 preferably includes a polishing grit made of an oxide or a carbide type grit.
The polishing film 24 preferably is includes at least one of Al2O3, SiC, and SiO2.
According to the above-noted configuration, the polishing plate is formed by a base plate, onto which is placed resilient sheet made of rubber having a uniform thickness, over the top of which is provided a polishing film that includes grit made of an oxide or a carbide polishing grit, thereby achieving a high polishing efficiency and enabling simultaneous adhesive agent removal and convex spherical surface polishing of the end surfaces of the ferrules.
Another aspect of the present invention, is a method of polishing the end face of a ferrule for an optical connector, this method comprising steps of (a) removing an adhesive agent 22 from the end face of a ferrule 10 and polishing the end face to a convex spherical surface by using a first polishing film 24A that includes an oxide or a carbide grit as a polishing member, and (b) performing finishing polishing of a convex spherical surface formed on the end face of the ferrule by using a second polishing film 24B that includes an oxide finishing agent.
According to the above-noted steps, by using an oxide or carbide grit as the polishing member, it is possible with just a first step of removing an adhesive agent from the end face of a ferrule and polishing the end face to a convex spherical surface and a second step of performing finishing polishing of the convex spherical surface formed on the end face of the ferrule, thereby facilitating the high-precise polishing of the ferrule end face without distortion. These polishing steps can be incorporated into either the polishing apparatus of the present invention or a general optical connector ferrule polishing apparatus.
The first polishing film 24A preferably includes at least one of Al2O3 and SiC.
The second polishing film 24B preferable includes SiO2.
By using the above-noted polishing grits, it is possible with an appropriate polishing efficiency, to polish a plurality of ferrule end faces without leaving large scratches on the end faces, and to do so without the need for expensive diamond polishing grit. Additionally, the convex spherical surfaces of the ferrule end faces are formed at one time, and it is possible to remove a work-changed layer caused by SiC or Al2O3 by merely using SiO2 for finishing. As a result, it is possible to simplify the polishing process, without using costly diamond grit, thereby providing not only a cost reduction, but also simplification of the polishing process.